The present invention relates to welding apparatus and in particular to control of welding operations in which gas is supplied to the welding none such as for example in gas xe2x80x98shieldingxe2x80x99 or gas xe2x80x98purgingxe2x80x99 operations.
Pressurised inert gas is frequently utilised in welding techniques to produce a preferred welding environment in which oxidization is inhibited in the weld and/or an optimum weld is produced by minimising porosity or other defects in the weld. Gas xe2x80x98purgingxe2x80x99 is a technique in which an inert gas is directed to provide an inert atmosphere on the under side of a weld.
Gas shielded arc welding is also a well known process in which the welding arc and the molten weld metal are protected from ambient air by means of a shielding gas or mixture of gases which may be inert (for example, argon or helium). Two varieties of the process using an inert gas are common, these being known as xe2x80x9cTungsten Inert Gasxe2x80x9d (TIG) and Metal Inert Gas (MIG). In TIG welding, the arc and a workpiece to be welded, whereas in MIG welding, the arc is maintained between a filler wire and the workpiece. When using an oxidizing gas, the process is known as metallic active gas (MAG). Combinations of inert gas and oxidizing gas are also possible.
Such welding processes rely upon a consistent supply of shielding gas to the welding zone. It has been found that there can be problems if the gas supply is interrupted, or, when a bottle or cylinder of gas reaches exhaustion. This can cause undesirable porosity to be formed in the weld when the gas shield is breached.
This problem is addressed in EP-A-0615809 which discloses a mechanical sensor a switch when the gas pressure falls below a predetermined threshold; opening the switch cuts off the welding wire advancing deice and the voltage source. The threshold at which the gas cut off occurs is determined by the spring constant of a biasing spring comprising the mechanical sensor.
Improved apparatus has now been devised.
According to a first aspect, the present invention provides welding control apparatus including:
i) a pressure sensor arranged to sense the pressure of a pressurised welding gas and produce a variable control output dependent upon the pressure level sensed;
ii) output connections for electrical connection to welding apparatus deliver means; and,
iii) control means for initiating a control signal to pass via the output driver connections when pressure of a predetermined level is sensed by the pressure sensor.
Because the output produced by the pressure sensor is variable to have a range between a maximum and a minimum, the predetermined level at which the control signal is initiated by the control means is variable over a range between a maximum and a minimum. This enables the gas pressure level at which the welding apparatus power supply to the driver means is cut to be varied. The control means preferably includes adjustment means for adjusting (preferably manually) the predetermined gas pressure level at which the control signal is initiated by the control means.
The apparatus can therefore be adapted to retro-fit a wide variety of different types of welding machines and apparatus in view of the fact that the pressure sensor output is variable. The adaptability of the control apparatus is further enhanced by providing a variable voltage regulator permitting connection to a range of welding apparatus voltage supplies. According to a second aspect, the invention therefore provides a retro-fit unit for connection to welding apparatus.
The adjustment means for adjusting the predetermined gas pressure level at which the control signal is initiated by the control means is preferably accessible from externally of the apparatus. The variable voltage regulator is preferably accessible from externally of the apparatus.
The pressure sensor preferably comprises an electronic pressure transducer arranged to produce a variable electronic output dependant upon the pressure sensed.
The electronic transducer comprises a thin film and diaphragm pressure transducer.
Desirably, the control means is arranged to initiate an output control signal as respective lower and upper threshold levels. This enables the welding driver means to be de-activated if gas at excess pressure is being delivered to the welding zone.
The apparatus preferably further comprises a conduit for the welding gas, the conduit being in communication with the pressure sensor.
The apparatus preferably comprises a connector having:
i) and inlet for pressurized welding gas;
ii) a plurality of outlets for pressurized welding gas.
According to a further aspect, the invention provides welding apparatus comprising:
(a) a supply of pressurized gas;
(b) a welding gun having an electrical power supply
(c) means for supplying welding filler material to the gun; and,
(d) a control arrangement including:
(i) a pressure sensor arranged to sense the pressure of the pressurized welding gas and produce a variable control output dependent upon the pressure level sensed;
(ii) output connections for electrical connection to welding gun power supply; and
(iii) control means for initiating a control signal when pressure of a predetermined level is sensed by the pressure sensor resulting in modification of the power status of the welding gun.
According to a further aspect, the invention provides welding apparatus comprising a connector having:
i) an inlet port for connection to a welding gas supply;
ii) a first outlet communicating with the inlet and arranged to enable welding gas to be delivered to a first location; and
iii) a second outlet communicating with the inlet and arranged to enable welding gas to be delivered to a second location.
A removable plug is preferably provided for at least one of the first and second outlet.
In use, with the plug in position closing one of the outlets, gas may be delivered from the gas supply to perform the xe2x80x98shieldingxe2x80x99 function. With the plug removed gas may be directed simultaneously via both outlets to perform simultaneous xe2x80x98purging xe2x80x99 and xe2x80x98shieldingxe2x80x99 functions.